Copolyamides from 1,6 or 2,6-naphthalene dicarboxylic acid

ABSTRACT

Synthetic fibers prepared from copolymers of hexamethylene diamine-adipic acid and hexamethylene diamine- 1-6- or 2,6naphthalene dicarboxylic acid are produced which are particularly useful in providing textile and reinforcing fibers.

United States Patent Ridgway et al.

[54] COPOLYAMIDES FROM 1,6 OR 2,6-

NAPHTHALENE DICARBOXYLIC ACID [72] Inventors: James S. Ridgway, Pensacola, Fla.; Henry L. King, Cary, NC; Oscar A. Pickett, Jr., Pensacola, Fla.

[52] U.S. Cl. ..260/78 R, 57/140'R, 152/330,

260/312 N, 260/334 R, 264/210 F [51] Int. Cl ..C08g 20/20 [58] Field of Search ..260/78 July 4,1972

[56] References Cited UNITED STATES PATENTS 3,538,056 11/1970 Caldwell ..260/78 R 2,296,555 9/1942 Hubert et al ....260/78 OTHER PUBLICATIONS Starr-Journal of Polymer Science, Vol. 4, (1966), Pt. A-l, pp. 3041- 3046 Primary Examiner-Harold D. Anderson Attorney-John W. Whisler and Stanley M. Tarter [5 7] ABSTRACT Synthetic fibers prepared from copolymers of hexamethylene diamine-adipic acid and hexamethylene diaminel-6- or 2,6- naphthalene dicarboxylic acid are produced which are particularly useful in providing textile and reinforcing fibers.

3 Claims, No Drawings COPOLYAMIDES FROM 1,6- OR 2,6-NAPHTI-IALENE DICARBOXYLIC ACID This application is a continuation-in-part of US. application Ser. No. 633,719, filed Apr. 26, 1967 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to synthetic linear fiber-forming copolyamides made from dicarboxylic acids and diamines. The invention further relates to yarns fabricated from these polyamide compositions.

2. Description of the Prior Art Polyamides, such as polyhexamethylene adipamide (nylon 66) and polycaproamide (nylon 6) are well known in the art and have found significant success as reinforcing fibers, such as tire cord. Although the tire cords obtained from the fiberforming polyamides heretofore known are of great value, much research is being continuously expended in order to improve the properties. For example, these previously known polyamides all possess the inherent drawback of flatspotting. Flatspotting is a term used to describe the out-of-roundness that occurs when a polyamide reinforced vehicle tire is allowed to stand for an extended period of time. That portion of the tire which is in contact with the road surface flattens and, when the vehicle is started again this fiatspot causes vibration of the vehicle and attendant passenger discomfort. While this phenomena of flatspotting is not completely understood, it is known that it is directly related to the stiffness instability or the relatively low modulus and high growth of polyamide yarns compared to other yarn materials.

Investigations have shown that the severity of flatspotting of tires reinforced with polyamide yarns is substantially reduced with yarns of increased stiffness or stiffness stability. Intrinsic chain stiffness (resistance to deformation) in classical physics is described in terms of Youngs modulus of elasticity and has a fundamental relationship to the chemical and physical constitution of a given polymer system. The ten'n modulus used herein refers to this intrinsic chain stiffness as described in Textile Research Journal, Volume 29, No. 7, page 525, July An object of the present invention therefore is to provide a fiber having increased stiffness stability.

Another object of the invention is to provide a yarn having good textile yarn properties in addition to increased stiffness stability.

SUMMARY OF THE INVENTION This invention provides a novel synthetic linear fiber-forming copolyamide from naphthalene dicarboxylic acid which has increased resistance to loss in stiffness (modulus) when subjected to conditions of heat and moisture and low shrinkage when subjected to hot or boiling water.

The copolyamides of the present invention are useful in the production of shaped articles by extrusion, molding or casting in the nature of yarns, fabrics, films, pellicles, bearings, omaments or the like. They are particularly useful in the production of textile fibers and as reinforcing cords produced therefrom.

The present invention provides a novel fiber-forming copolyamide composed of (A) 80 to 90 mole percent, based on the molecular weight of the copolyamide, of units represented by the structure (B) to mole percent, based on the molecular weight of the copolyamide, of units represented by the structure wherein R is tetramethylene.

Polyamides prepared from hexamethylenediamine, adipic acid, and 1,4-naphthalene dicarboxylic acid or l,8- naphthalene dicarboxylic acid are described in the prior art (U.S. Pat. No. 2,296,555). However, these polyamides, by virtue of containing the 1,4- or l,8-naphthalene dicarbonyl linkages rather than the l,6- or 2,6-naphthalene dicarbonyl linkages, have properties substantially different from the polya mides described herein and are not suitable for providing high quality textile and reinforcing fibers. Polyamides formed from l,8-naphthalene dicarboxylic acid tend to have low molecular weights when melt polymerized and are not easily melt spun into fibers due to the close proximity of the carboxyl groups that cause the acid to behave as a chain terminator. On the other hand, the molecules of polyamides formed from 1,4- naphthalene dicarboxylic acid do not pack or fit well due to both carboxyl groups being on the same ring; a poor fit of the moleculescauses high boiling water shrinkage properties that is generally undesirable in monocomponent textile fibers. In contrast the polyamides described herein do not suffer from either of the disadvantages inherent in polyamides formed from 1,4- or l,8-naphthalene dicarboxylic acids.

In a typical preparation, the copolyamide is formed by interpolymerizing (A) substantially equimolecular proportions of adipic acid and hexamethylene diamine, (B) substantially equimolecular proportions of a naphthalene dicarboxylic acid and hexamethylene diamine wherein component (A) is present in an amount sufi'icient to provide to mole percent of the final copolymer and component (B) is present in an amount sufi'rcient to provide 10 to 20 mole percent of the final copolymer. It will be understood that the designation equimolecular proportions" of the diamines and the diacids includes the preformed salt reaction products thereof. It is of course obvious that the total mole percentage will not exceed mole percent. The copolyamides of this invention in which the components are present in the amounts defined have been found to possess the properties desired.

The copolyamides of this invention are prepared by procedures well known in the art and commonly employed in the manufacture of simple polyamides. That is, the reactants are heated at a temperature of from C. to 300 C. and preferably from 200' C. to 295 C. until the product has a sufficiently high molecular weight to exhibit fiber-forming properties, which properties are reached when the copolyamide has an intrinsic viscosity of at least 0.4. The reaction can be conducted at superatmospheric, atmospheric or subatmospheric pressure. Often it is desirable, especially in the last stage of the reaction, to employ conditions, e.g. reduced pressure, which will aid in removal of the reaction by-products. Preferably the reaction is carried out in the absence of oxygen, for example, in an atmosphere of nitrogen.

Intrinsic viscosity [1 as employed herein is defined as in which 1;, is the relative viscosity of a dilute solution of the polymer, in the same units at the same temperature and C is the concentration of grams of polymer per 100 cc. of solution and the measurements are made at 30 C., the solvent being either formic acid or m-cresol.

The naphthalene dicarboxylic acids which are employed in the preparation of the copolyamides of the present invention may be represented by the formula:

Lil-naphthalene dicarboxylic acid DESCRIPTION OF THE PREFERRED EMBODIMENTS ln order to illustrate the invention and the advantages thereof with greater particularity, the following specific examples are given. It is to be understood that they are intended to be only illustrative and not limitative. Parts are given by weight unless otherwise indicated.

As with conventional nylon production, various additives may be introduced into the polymer for purposes of delustering, stabilization toward heat and the like. Additives for these and other like purposes are well known in the art.

EXAMPLE I Polyamide From Adipic Acid and Hexamethylene Diamine This example is illustrative of a typical method for preparing polyamides and is cited as the control example (nylon 66).

Two general methods are known to the art for preparing salts of diamines and diacids. Method 1): if both the diamine and the acid are water soluble, an aqueous salt is prepared by adding a solution of the diamine to a slurry, or solution, of the acid in water. Equimolar amounts of diacid and diamine are used. The salts are precipitated by addition of an alcohol such as methanol or ethanol. Method (2): 1f the diamine or diacid is difficulty soluble or insoluble in water, dioxane is used as solvent. Alcohol is used to precipitate the salt. The salt is washed thoroughly, redissolved and the solution is treated with activated charcoal to remove colored impurities prior to recrystallization.

The polymerization reaction was conducted in an autoclave by charging 400 parts of salt from hexamethylene diamine and adipic acid prepared by Method (1), and sufficient water to give a solution of 50 percent solids. The autoclave was carefully purged with an inert gas and the heating cycle started. The salt solution was heated to 200 C. and 250 psig. The pressure was held at 250 psig as water was removed. After about 60 minutes the pressure was gradually released to atmospheric the temperature increased to about 280 C. or above the melting point of the polymer. This temperature was held approximately 30 minutes after which a 0.020 inch l-hole spinneret was attached and the molten polymer was extruded, quenched in water and wound-up at about 160 rpm. The yam was cold drawn at a ratio of 4-5 times to a denier of about 10.

2,6-naphtha1ene dicarbox ylie acid and 2,6-Naphthalene Dicarboxylic Acid Two salts were prepared following Method l given in the above Example 1. Salt was prepared from hexamethylene diamine and adipic acid and a second salt was prepared from hexamethylene diamine and 2,6-naphthalene dicarboxylic acid.

1. Salts were mixed to give 90 mole percent 66 (hexamethylene diamine-adipic acid) and 10 mole percent 6 NDA (2,6) (hexamethylene diamine-2,6-naphthalene dicarboxylic acid Polymerization was carried out as shown in Example I.

The fiber had a tenacity of 6.54 gpd, breaking elongation of 27.5 percent and an initial modulus of 40 gpd. The polymer melted at 246 C. and had an intrinsic viscosity [1;] of 1.04 measured in formic acid.

2. A second fiber was prepared from the same raw materials by mixing salts to give mole percent 66 and 20 mole percent 6 NDA (2,6) and polymerized as above. The fiber had a tenacity of 6.00 gpd, breaking elongation of 26.8 percent and an initial modulus of 43 gpd. The polymer melted at 244 C. and had an intrinsic viscosity [1 of 0.76 measured in formic acid.

EXAMPLE lIl Copolyamides From Adipic Acid, Hexamethylene Diamine and 1,6-Naphthalene Dicarboxylic Acid The salts were prepared from hexarnethylene diamine and adipic acid and from hexamethylene diamine and 1,6- naphthalene dicarboxylic acid by Method 1 given above.

1. The above salts were mixed to give mole percent 66 and 10 mole percent 6 NDA 1,6). Polymerization was carried out following the standard procedure. The fiber had a tenacity of 4.17 gpd, a breaking elongation of 12.4 percent and an initial modulus of 52 gpd. The polymer melted at 259 C. and had an intrinsic viscosity [1 of 0.7 1 7 measured in m-cresol.

2. The above salts were mixed to give 85 mole percent 66 and 15 mole percent 6 NDA 1,6). Polymerization was carried out following the standard procedure. The fiber had a tenacity of 5.15 gpd, a breaking elongation of 9.6 percent, and an initial modulus of 46 gpd. The polymer melted at 253 C. and had an intrinsic viscosity [1;] of 0.71 measured in m-cresol.

Samples of fibers from the above examples were tested for modulus (stiffness) stability under conditions of moisture and heat. Testing was performed by following the change in Sonic Modulus. The term sonic-modulus" as used herein refers to the dynamic mechanical modulus obtained by the velocity of sound measurements determined by the method disclosed by W. H. Charch and W. W. Moseley, Jr. in the Textile Research Journal, Vol. 29, No. 7, page 525, July, 1959. Data from these tests are listed in Table 1, as change in sonic modulus E, with increasing temperature and relative humidity.

TABLE 1 Comparison of lleat and Moisture on Fiber Modulus (Sonic Modulus-E.)

Relative humidity, 0 percent Relative humldity 30 percent 80 0. 0. C. 75 C 90 C 30 0., Percent Percent Percent 30 C Percent Percent E. s, ret. ret. E. ret. E, E. ret. E, ret.

Nylon 66 (control) 5U 47 80 37 63 1) 33 75 43 57 36 48 66-10 1\1%G(2,6-N1)A) 53 41 77 3G (is 23 44 57 311 64 32 55 66-20 M% (1 (2,0-N DA) 53 47 .10 43 X1 23 44 (i2 40 (S4 34 55 (36-5 M% (i(1,0-NDA).. 51') 45 81 37 (i7 23 42 (S2 41 (i6 32 51 (36-10 M% 6(1,(3N DA) 5U 45 81 2!! 70 22 40 G2 42 (37 32 51 (56-15 114% (i (LG-NDA) t 50 45 81 41 73 26 411 59 43 72 34 58 The yarn had a tenacity of 6.67 gpd, a break elongation of 70 17.5 percent and an initial modulus of 39 gpd. The polymer melted at 262 C.

EXAMPLE 11 Polyamides From Adipic Acid, Hexamethylene Diamine 7 vcord.

EXAMPLE V Two salts were prepared as in Example 11 following the procedure in Method (1) of Example 1. Three fibers were prepared from the salts by mixing the salts in the mole proportions specified in Table 2 and polymerizing each mixture as described in Example I. The boiling water shrinkage of each of the monofilaments was determined by exposing each filament to boiling water for 5 minutes and measuring its length both before and after exposure. The percent boiling water shrinkage was then determined by the following formula:

length before exposurelength after exposure length before exposure the results of each determination are given in Table 2 in which the following abbreviations are used:

C i? t 6 (2,6-NDA) NH (CH2) oNHC- The results given in Table 2 show that fibers prepared from polyamides of the invention have surprisingly low boiling water shrinkage. Textile fabrics made from these fibers can be laundered with a minimum of shrinkage.

By way of comparison, neither 1,4- nor 1,8-naphthalene dicarboxylic acid is considered to be a useful monomer for the preparation of fiber-forming polyarnides due to their structure,1.e.,

units do not have the desired fiber-forming symmetry and til

units tend to form imide structures.

What is claimed is:

1. A fiber-forming copolyamide consisting of from (A) to mole percent, based on the molecular weight of the copolyamide, of recurring units of the structure and of from (B) 10 to 20 mole percent, based on the molecular weight of the copolyamide, of recurring units of the structure selected from the group consisting of and 0 I 5 NH(CH2)0NHC 2. The copolyamide of claim 1 wherein (B) is H O u NH(CH:)0NHC 3. The copolyamide of claim 1 wherein (B) is 

2. The copolyamide of claim 1 wherein (B) is
 3. The copolyamide of claim 1 wherein (B) is 